A turbomachine turbine, in particular a low-pressure turbine, comprises a plurality of stages, each having a rotor wheel mounted to rotate in a cylindrical or frustoconical ring formed by sectors that are fastened together end to end circumferentially on an outer casing of the turbine, and a nozzle located downstream from the wheel and formed by an annular row of stationery vanes carried by the outer casing (FR-A1-2 899 273 in the name of the Applicant).
Hot gas under pressure leaving the combustion chamber of the turbomachine passes between the vanes of the nozzles and flows over the blades of the turbine wheels, thereby having the effect of raising the temperature of the rings.
In known manner, each ring sector presents a downstream end that is kept bearing radially against a cylindrical casing rail via the nozzle. The nozzle has an upstream cylindrical rim for attaching to the casing rail, the rim bearing radially against an outer cylindrical surface of the rail, which has its inner cylindrical surface bearing radially against the downstream ends of the ring sectors. Having the casing rail bear radially against the downstream ends of the ring sectors serves to position the ring sectors radially relative to the casing. Furthermore, the downstream ends of the ring sectors bear axially against the casing rail to provide sealing in operation.
The areas of contact both between the casing rail and the ring sectors and between the casing rail and the nozzle sectors are relatively large, and they form means for conducting heat both between the ring and the casing and between the nozzle and the casing. The casing may thus reach a high temperature that runs the risk of weakening it and of shortening its lifetime.
Furthermore, in operation, the nozzle sectors transmit forces to the casing rail, which rail is subjected to relatively large tangential stresses in its downstream end portion, thereby giving rise to a phenomenon of creep in the casing rail. These tangential stresses are in addition to the above-mentioned thermal stresses and they reduce the lifetime of the casing rail considerably.